The present invention relates to an image sensor free from undesirable incident light rays which have not been reflected in the surface bearing the image to be sensed and a method of manufacturing the same.
Along with the efforts to decrease the sizes of facsimile machines, photo-copying machines and the like, contact image sensors, as a very small photoelectric conversion sensor, have attracted interest of the researchers.
An exemplary conventional image sensor is illustrated in FIG. 1(A). The sensor comprises a glass substrate 1, a front light blocking electrode 2, a photosensitive semiconductor film 3a, a rear transparent electrode 4, a lead electrode 5 for taking out output signals and a transparent protector layer 6 which is to make direct contact with an original 7. A light window 10 is opened in the photoelectric conversion structure consisting of the electrodes 2 and 3 and the semiconductor film 5. Light rays 8 passed through the light window 10 are reflected by the original 7 and absorbed by the semiconductor film 3a with the visual information contained in the original 6. Another exemplary image sensor is illustrated in FIG. 1(B). This sensor comprises similar elements as the above example except that the lead electrode 5 extends over the upper surface of the photosensitive semiconductor film 3b and divided into two parts between which photogenerated signals are produced. A light window is opened in the lead electrode 5 in order to provide an access to the semiconductor film 3b. In these structure, the light blocking electrodes 2 have to be formed extending beyond the semiconductor films 3a or 3b at 9. The extending portion 9 is provided for preventing incident light from directly entering the semiconductor film without reflection on the original 7.
The photoelectric conversion structures are formed by patterning the triple-layered laminae consisting of the electrodes 2 and 4 and the semiconductor film 3. Particularly, due to the extending portion 9, the light blocking electrode 2 cannot be patterned together with the semiconductor film. This increases the number of process steps.